USB controllers get deregistered at boot time
 

I noticed that my 2 USB controllers get deregistered near the end of the bootup process. Here is the dmesg:

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usb-uhci.c: USB UHCI at I/O 0xb400, IRQ 5
usb-uhci.c: Detected 2 ports
usb.c: new USB bus registered, assigned bus number 1
hub.c: USB hub found
hub.c: 2 ports detected
PCI: Found IRQ 9 for device 00:1f.4
PCI: Setting latency timer of device 00:1f.4 to 64
usb-uhci.c: USB UHCI at I/O 0xb000, IRQ 9
usb-uhci.c: Detected 2 ports
usb.c: new USB bus registered, assigned bus number 2
hub.c: USB hub found
hub.c: 2 ports detected
usb-uhci.c: v1.275:USB Universal Host Controller Interface driver
usb.c: USB disconnect on device 00:1f.2-0 address 1
usb.c: USB bus 1 deregistered
usb.c: USB disconnect on device 00:1f.4-0 address 1
usb.c: USB bus 2 deregistered
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Is that the reason why I don't get any numbered directory when I 'ls /proc/bus/usb', even though I 'mount -t usbdevfs none /proc/bus/usb'?

Could you please help?